This invention relates to a serial pulse frequency converter of the type adapted to convert a pulse train from a transducer in a vehicle driveline at a first frequency indicating vehicle speed to a pulse train at a proportional second frequency for use by a vehicle mounted electronic speedometer. Increased use of such electronic speedometers with a variety of transducers and driveline designs has produced the potential for a proliferation of specialized vehicle speedometer cluster assemblies, with each assembly being adapted for a different proportionality constant between vehicle speed and the corresponding pulse frequency output of the transducer in the particular driveline. A serial pulse frequency converter enables a single speedometer cluster to be used with a variety of transducers having different ratios of vehicle speed to output pulse frequency.
Most commercially available pulse frequency converters allow only conversion ratios which are countdowns of 256 or other powers of two. A practical device for the described application, however, requires finer control over the conversion ratio. One prior art device, an example of which is shown in U.S. Pat. No. 3,835,396, issued Sept. 10, 1974 to Demos et al, counts high frequency clock pulses between input pulses, multiplies and divides the count by constants defining a proportionality ratio and downcounts the transformed count by high frequency clock pulses to produce output pulses. This is the general approach to the problem used by the apparatus of this invention. However, the apparatus of this invention is an improvement on the prior art apparatus.